1. Field of the Invention
The present invention relates to a method and an apparatus for processing or machining a workpiece using a plurality of laser beams having different wavelengths.
2. Description of the Related Art
FIG. 18 is a schematic diagram illustrating a prior-art apparatus for processing a workpiece using a plurality of laser beams having different wavelengths. Referring to FIG. 18, a phase grating G1 is employed to split a laser beam of wavelength xcex1 into a diffraction beams shaped in a designed array. The diffraction beam array is introduced into a condenser lens L1, then passes through an optical path combining mirror 3, and then converges to impinge on processing points of a workpiece 5. In addition, a phase grating G2 is employed to split a laser beam of wavelength xcex2 into another diffraction beam array. The diffraction beam array is introduced into a condenser lens L2, then reflected upon the optical path combining mirror 3, and then converges to impinge on the processing points of the aforementioned workpiece 5.
In this case, the diffraction beams of wavelengths xcex1 and xcex2 are focused on the same spot of the workpiece 5, thereby making it possible to allow the diffraction beam array of wavelength xcex1 to heat the workpiece 5 and the diffraction beam array of wavelength xcex2 to make holes or the likes in the workpiece 5. Processing a workpiece with a plurality of laser beams having different wavelengths at the same time as described above can improve both process quality and process yield.
However, as shown in the foregoing, diffraction beam arrays generated from a plurality of laser beams having different wavelengths have to impinge on targeted positions on a workpiece. For this purpose, it is necessary to provide a phase grating and a condenser lens for each laser beam having a different wavelength, and also dispose an adjustment unit (not shown in the figure) for adjusting the attitude and position of these elements. For this reason, the whole assembly is made complicated. In addition, the adjustment with such units is time-consuming and labor intensive to desired conditions for optimization of diffraction, thereby increasing processing costs. It is also necessary to provide an optical path combining mirror or the like between a condenser lens and a workpiece. This adds constraints to the arrangement and the specification of the optical system. Accordingly, there is a problem of making it difficult to adjust the diameter of focal spots and their intervals on the workpiece to predetermined conditions (for optimization of diffraction beam array conditions).
Furthermore, when a single laser is used which emits two or more laser beams of different wavelengths simultaneously, such a complicated arrangement has to be employed in which two beams provided on the same axis are once separated, then each of the beams is split by the splitter element, and then the split beams are combined again on the surface to be machined. As such the advantages of employing one laser instead of two lasers were not fully taken.
The present invention was developed to solve these problems. The object of the present invention is to provide a method for laser beam machining and an apparatus for implementing it that has a simple optical system to perform machining by using a plurality of laser beams of different wavelengths. In addition, the optical system is allowed to be adjusted and the laser beam array condition to be optimized in a simpler manner.
The present invention includes the steps of splitting a plurality of laser beams of different wavelengths into diffraction beams in designed arrays, respectively, by using a common phase grating, and directing those diffraction beams to a workpiece to focus and impinge on processing points of the workpiece to thereby process it. This makes it possible to reduce the number of phase gratings for splitting laser beams involved in the processing. Accordingly, the arrangement of the processing apparatus is simplified, thereby facilitating the adjustment of the optical system and the optimization of diffraction beam array conditions.
Furthermore, according to another aspect of the present invention, the diffraction beams of different wavelengths are directed to impinge on the same position on the workpiece. For example, this makes it possible to allow diffraction beams of one wavelength to heat portions of a workpiece to be processed and diffraction beams of another wavelength to make a hole or cut in these portions. In this case, it is possible to provide a beam adjusting unit for adjusting the diameter of each laser beam in its optical path so that the diffraction beams focused at the processing points on the workpiece may have the same diameter at each of these points.
Furthermore, according to another aspect of the present invention, the diffraction beams of an emitted laser beam are designed so as to have almost the same intensity. This makes it possible to perform uniform laser processing at a plurality of positions at the same time.
Furthermore, according to another aspect of the present invention, the phase grating is shifted along the optical axis of the system to adjust the impinging positions of the diffraction beams on the workpiece. This makes it possible to adjust the diameter and the interval of the focal spots of the diffraction beams for their requirement, thereby allowing for any desired processing with high accuracy.
Furthermore, according to another aspect of the present invention, two lasers of different wavelengths are used. This, among others, provides a fundamental arrangement and enables the apparatus to be substantially simplified in terms of its configuration and control as well.
Furthermore, the present invention provides a laser processing apparatus. The apparatus includes a laser means consisting of at least a single laser for emitting a plurality of laser beams of different wavelengths, a common phase grating for splitting each of the laser beams of different wavelengths into diffraction beams in a designed array, respectively, and a beam condenser for focusing the diffraction beams or laser beams incident upon the phase grating. According to this apparatus, the number of the phase gratings for splitting laser beams is reduced to simplify the apparatus, thereby facilitating the adjustment of the optical system and the optimization of the diffraction beam array conditions.
In the aforementioned case, the apparatus may be equipped with a single laser that emits a plurality of laser beams of different wavelengths. Alternatively, the apparatus may be equipped with plural lasers, each of which emits a laser beam so as to provide the plurality of laser beams of different wavelengths.
Furthermore, the laser beams of different wavelengths can be two lasers of wavelengths xcex1 and xcex2, satisfying that m1xcex1=m2xcex2, where m1 and m2 are the diffraction orders of beams split by the phase grating. This makes it possible for two diffraction beam arrays produced from these laser beams of the two wavelengths to strike the workpiece at same points on it.
Furthermore, according to another aspect of the present invention, the apparatus has a beam adjusting unit for adjusting the diameter of a laser beam emitted from the laser means, disposed in its optical path to the phase grating. According to this apparatus, the focal spot diameter of diffraction beams on the workpiece can be adjusted. Therefore, even if using a plurality of laser beams of different wavelengths, the apparatus makes it possible to perform processing with high accuracy and high efficiency.
Furthermore, according to another aspect of the present invention, the apparatus is configured in the way that the phase grating can be positioned in the direction of the resultant optical axis after the emitted laser beams combined. This makes it possible to adjust the impinging positions of the diffraction beams on the workpiece and to perform processing with an considerably high accuracy.
Furthermore, according to another aspect of the present invention, the condenser is provided to be achromatic. In the case of using several laser beams of different wavelengths, for example, two kinds of wavelengths, the condenser can be endowed with the same focusing distance for those two wavelengths.
Furthermore, in the case of using a laser that emits pulses of different wavelengths at the same time, a spectroscopic means for passing individual pulses of different wavelengths during a specific time window prepared for each wavelength is disposed between the laser and the phase grating. This makes it possible to irradiate the workpiece alternately with diffraction beam arrays of different wavelengths.